Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$242.84	3.103%	$250.3753	$250.38	$250.40	$250.40
Purchase #2	$28.34	12.339%	$31.8369	$31.84	$31.85	$31.80
Purchase #3	$33.38	11.328%	$37.1613	$37.16	$37.15	$37.20
Purchase #4	$56.46	9.547%	$61.8502	$61.85	$61.85	$61.90
Purchase #5	$213.43	11.522%	$238.0214	$238.02	$238.00	$238.00
Purchase #6	$88.42	7.401%	$94.964	$94.96	$94.95	$95.00
Purchase #7	$123.63	7.215%	$132.5499	$132.55	$132.55	$132.50
7 purchase totals =	$786.50		$846.7590	$846.76	$846.75	$846.80